Hand-held dental devices with a light source and an energy source like an accumulator have been known for a long time in dental technology. An example of this is the dental device disclosed in DE 42 11 230 A1 and corresponding U.S. Pat. No. 5,471,129, which is hereby incorporated by reference, in which the light source is powered by rechargeable accumulators.
Cordless light curing devices should not be too heavy, if possible.
Dentists and dental technicians are striving for polymerization cycles to be as short as possible. High-performance LED chips have become available for this in the meantime which allow for light emission cycles of e.g. 20 or 30 seconds.
DE 10 2004 033 699 A1, which is hereby incorporated by reference, discloses a cordless light curing apparatus which is provided with an Ultra-Cap-Capacitor as an energy storage unit. This Ultra-Cap-Capacitor was able to supply the LED chips which were available at that time with enough energy so that 6 or 7 polymerization cycles were possible until the Ultra-Cap-Capacitor had to be recharged.
In the case of too little energy the problem is that the available charge quantity is not sufficient for one polymerization cycle, and this would lead to the fact that non-polymerized monomers would stay in the lower layers of the dental restoration part which is considered very critical as free radicals are suspected to be carcinogenic.
This becomes even more critical as the power of LEDs reaches up to 10 Watts currently, so that even one polymerization cycle might lead to the danger that the charge quantity stored is not sufficient when the local Ultra-Cap-Capacitor has not been charged sufficiently.
A further example of such light curing devices with an Ultra-Cap-Capacitor that have been known for a long time now, is evident from WO 2010/029519, which is hereby incorporated by reference. In this solution, too, the Ultra-Cap-Capacitor that is to replace the batteries known from the prior art, is charged with the aid of a charging device, and is then intended to emit the desired power for the operation of the light source.
Especially with hand-held light-curing devices, in particular pencil-shaped hand-held light-curing devices, the space available for the accommodation of the Ultra-Cap-Capacitor is limited, and the hand-held light-curing device must not be too heavy either.
Attempts have been made to increase the specific power density by using capacitors whose rated voltage is exactly the charge voltage in order to thus realize a capacity as large as possible. In this respect it is disadvantageous, however, that no voltage reserve is available and also that in case of a tolerance of the capacitors, those highly-sophisticated electronic components are overloaded.
In dental practices an explosion of a capacitor would have disastrous consequences, since the materials used in the capacitor are highly toxic and—should the situation arise—would be absorbed by the patient via the mucous membranes thereof.
A further problem of the light curing devices with an Ultra-Cap-Capacitor that have been known for about ten years now, is the necessity to make available a light curing device in the dental practice that is ready to be used any time.
If, for instance, after the light curing of the dental material to be polymerized, which has been applied by the dentist in several layers whereas each layer has been cured at least partially, the dentist discovers that the final curing should take place now, there may not be available enough energy in the Ultra-Cap-Capacitor anymore.
A partial light curing with insufficiently charged capacitors, however, results in the curing of the top layers only, and the lower layers remain uncured for the time being. However, later, in post-curing, these layers contract so that the dental restoration shrinks laterally which leads to the extremely undesired formation of marginal gaps.
Therefore, it is important that enough energy is available for final curing which is typically supposed to take longer than the partial curing of the individual incremental layers of the polymerisation material. Typically, however, the Ultra-Cap-Capacitor has the lowest energy reserves exactly when the demand is highest which can lead to critical situations and rights of recourse towards the dentists.
In order to avoid this it has become established to always make available two light curing devices when using such light curing devices wherein one serves as a reserve in such a situation.
On the other hand, this results in substantial additional costs.